Fix broken links flagged by the docs link checker

What does this MR do?

The check_links job is allowed to fail, and it's been failing on main with 11 broken links. I checked each one against the source and against production, and they fall into three groups.

1. Seven https://design.gitlab.com/tailwind-documentation/<utility>/ links in components/tailwind_config_viewer.vue. Those pages return 200 in production, but the Tailwind documentation is a separate Pages deployment, so the local server the checker scans returns 404 for everything below the root. The skip pattern in scripts/check_links.mjs only covered the root path, so I widened it to the whole prefix.
2. https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/issues on the CSS foundations page. That URL now returns 404 to anonymous visitors (so does https://gitlab.com/gitlab-org/gitlab/-/issues). I pointed it at https://gitlab.com/gitlab-org/gitlab-services/design.gitlab.com/-/work_items, which is the list that replaced it, and made the same change in .claude/skills/css/SKILL.md.
3. [Multi step form template](components/form-multi-step) on the path, progress bar, and forms pages. The link had no leading slash, so it resolved relative to the current page. I added the slash. The progress bar page wasn't in the report, but it has the same bug.

Nothing under packages/* changed, so there's no changeset.